Proton magnetic resonance spectra of amino-acids and peptides relevant to wool structure. Part IV. Relative residence times of dipeptides and tripeptides of phenylalanine and tyrosine

Abstract

100 MHz High resolution ¹H n.m.r. spectra have been recorded from acidic (pD 0.6–1.4) and basic (pD 12.3–13.1) D₂O solutions of the dipeptides Gly-Phe, Ala-Phe, Val-Phe, Met-Phe, Leu-Phe, Phe-Leu, Phe-Val, Phe-Tyr, His-Phe, Gly-Tyr, Ala-Tyr, Val-Tyr, L-Leu-Tyr, D-Leu-Tyr, Trp-Tyr, Trp-Gly, and Tyr-Val, within the range 300–360 K. Iterative analyses of ABC/ABX systems have yielded coupling constants from which relative populations of C_α–C_β rotamers have been derived. 100 and 220 MHz ¹H spectra have similarly been analysed for the basic and acidic D₂O solutions of the tripeptides Gly-Phe-Met, Met-Phe-Gly, Gly-Phe-Ala, Gly-Phe-Phe, Gly-Tyr-Gly, and Val-Tyr-Val, within the range 280–360 K. In acid, the trans-rotamer (ring opposed to carboxyl or C-terminal peptide group) is favoured for dipeptides of the types X-L-Phe and X-L-Tyr and for the tripeptides Gly-Phe-Ala and Gly-Tyr-Gly; in base, the trans-rotamer predominates in most peptides.